As the adjustment mechanism for use in performing a focus adjustment or zoom adjustment in this type of lighting device in the prior art, it is well known to provide such a structure as one in which a lens holder for holding a lens is supported in such a way that the holder can be slid in a forward or rearward direction along the optical axis, a knob slid together with the lens holder is arranged at an outer surface of a lighting device, the knob is formed by a screw member threadably engaged with the lens holder, the lighting device is held together with the lens holder under a state in which the screw is fastened to lock its motion and in turn it can be slid under a state in which the screw is loosened.
However, the adjustment work with such a prior art adjustment mechanism as described above is carried out such that the screw is once loosened, the lens is slid together with the knob, after its position is adjusted, the screw is fastened to fix the lens position, so that there may be present a possibility that the work is troublesome and at the same time the lens position is displaced when the screw is fastened.
In addition, there is also present the adjustment mechanism utilizing a rack and pinion as shown in FIG. 13. This mechanism is constructed such that a rack 103 having a lens holder 102 fixed thereto is engaged with a pinion gear 101 turned under a rotating operation of an adjustment knob (not shown) rotated at its specified position, the rack 103 engaged with the pinion gear 101 is slid by the rotation of the adjustment knob at its specified position, resulting in the lens holder 102 being slid in a forward or rearward direction.
In accordance with such a mechanism as above, the adjustment knob is placed at its specified position, so that the lens position cannot be acknowledged from outside part of the lighting device 104 and an operator performs a position adjustment while looking at the lighting plane and it may produce a problem that a skill is needed for the fine adjustment.
When the bulb 105 has a high capacity in this type of lighting device, the thermal influence at a location of the reflector 106 which is the nearest to the filament 107 is increased and there is a possibility that the base material of the reflector 106 will become cracked or the raw material coated on the base material will peel.
In this type of lighting device described above, a gobo having various kinds of patterns opened and formed in a metallic thin plate by a punching work or an etching work is usually used for increasing a stage effect. Then, several types of gobos with different outer diameter sizes are prepared even though the gobos have the same patterns to each other, and they are separately used in response to object.
Due to this fact, several types of gobo holders corresponding to gobo sizes used for installing a gobo in the lighting device are prepared, the holder is selected in compliance with the size of gobo and applied for its use.
The gobo holder is constructed such that two metallic plates are overlapped to each other to enable the gobo formed by a metallic thin plate to be engaged and held between themselves, and the gobo is used while being inserted between the two plates of the gobo holder.
However, operations for selecting and using the gobo holder in compliance with a size of the gobo to be used are troublesome and substantially influence a workability of the gobo showing a high degree of repetition in use.
This invention has been invented in view of the aforesaid circumstances as found in the prior art and it is a first object of the present invention is to provide a lighting device having a novel lens position adjusting mechanism capable of easily performing a fine adjustment of a lens position when the lens is slid in a forward or rearward direction along the optical axis to perform a focus adjustment or a zoom adjustment and further a fixing of the lens position after adjustment can be easily performed.
It is a second object of the present invention to provide a lighting device capable of restricting influence against a reflector caused by heat generated by a bulb as much as possible.
It is a third object of the present invention to provide a lighting device having a gobo holder which can be adapted for two types of gobos of different sizes having a high degree of repetition in use (an amount of distribution) by one gobo holder.